The present invention relates generally to fasteners and more particularly to manufacturing of a polymeric fastener having a spiral formation.
Traditionally, polymeric parts are made by injection or extrusion molding. In such processes, a heated polymeric liquid is inserted into match metal dies under high pressure, after which the dies are internally cooled in order to cure the manufactured parts. Air is vented from the die cavity when the molten polymer is injected therein. Injection and extrusion molding are ideally suited for high volume production where one hundred thousand or more parts per year are required. These traditional manufacturing processes, however, disadvantageously require very expensive machined steel dies, which are difficult and time consuming to modify if part revisions are desired, and are subject to problematic part-to-part tolerance variations. Such variations are due to molding shrinkage during curing, molding pressure differences, part warpage due to internal voids and external sink marks, and the like. The expense of this traditional die tooling makes lower volume production of polymeric parts prohibitively expensive.
Exemplary injection molded clips are disclosed in U.S. Pat. No. 5,829,937 entitled “Tolerance Clip” which issued to Morello et al. on Nov. 3, 1998, and U.S. Pat. No. 5,505,411 entitled “Harness Fixing Device” which issued to Heaton et al. on Apr. 9, 1996; both of which are incorporated by reference herein. These clips are of a Christmas tree variety having spaced apart and separated barbs extending from each side of a stem. These clips, however, only provide limited and finite workpiece fastening positions due to the barb spacing. Therefore, this prevents a tightly fastened joint. Furthermore, U.S. Pat. No. 6,336,779 entitled “Fastening System,” which issued to Jakob et al. on Jan. 8, 2002, discloses a plastic screw; this screw, however, disadvantageously is only suited for rotational engagement of its thread with a workpiece panel.
It is also known to use stereolithography to produce non-functional polymeric parts other than fasteners. Such conventional stereolithography methods use a laser to create a layered part on a moving platform within a vat of liquid polymer. The part rises from the liquid as it is being made. These parts are extremely slow to produce and impractically brittle.
In accordance with the present invention, a fastener is provided. In another aspect, a spiral fastener, is made of layers of material and/or a light curable material. Another aspect uses a three-dimensional printing machine to emit material from an ink jet printing head to build up a fastener having a spiral formation. A further aspect provides a method of making a spiral fastener by depositing material in layers and/or a built-up arrangement. Yet another aspect makes a spiral fastener by depositing material in an environment where the fastener is essentially surrounded by a gas, such as air, during the material deposition. In another aspect, a linearly insertable, polymeric fastener includes a flexible spiral formation having a continuous undercut or groove between the thread and a central shaft. A method of making a fastener with a spiral formation is also employed in another aspect.
The present spiral fastener and method are advantageous over traditional devices. For example, when three-dimensionally printed, the present spiral fastener and method do not require any unique tooling or dies, thereby saving hundreds of thousands of dollars and many weeks of die manufacturing time. Furthermore, the present three-dimensional printing method allows for quick and inexpensive design and part revisions from one manufacturing cycle to another. In another aspect, part-to-part tolerance variations are essentially non-existent with the presently printed spiral fastener and method such that at least ten, and more preferably at least forty, identical spiral fasteners can be produced in a single machine manufacturing cycle. For other aspects of the presently printed spiral fastener and method, multiple head openings, a stationary support for the built-up fasteners within the machine, and the ambient air manufacturing environment allow for increased manufacturing speed, simpler machinery and ease of access to the manufactured fasteners. It is greatly advantageous that the present polymeric fastener includes a continuously spiraling and tapering workpiece-engagement formation extends around a stem, which provides essentially infinite positioning relative to an attached workpiece of varying thicknesses and hardnesses. For example, the same fastener has a flexible spiral engagement formation or fin which can accommodate a metal panel having a 2 mm thickness and a plaster board panel having a 4 mm thickness. It is also beneficial that the present polymeric spiral fastener is linearly inserted into a workpiece rather than the more time consuming rotation of conventional screws. Additional advantages or features of the present invention can be found in the following description and appended claims as well as in the accompanying drawings.